We just bought a single-story house that was originally the upper-level of a two story house. Original build date is listed at 1946.

The story told to us (and confirmed by all the neighbors) was that the home was originally in a different location. The first story burned, and the owner at the time (back in the late 1960's) cut the second story off the first, and moved the house to a new location onto a foundation, where the house has currently sat for the last 40+ years.

We just tried to have cable installed with lines running under the house. The guys tried to snake the line and crawled under the house only to find they could not pull the lines through because there is a drywall/plaster ceiling nailed to at least 1/2 of the underside of our floor joists! We now realize the people who originally moved the house must have never actually removed the drywall/plaster ceilings from the first story.

How on earth do I have this removed? If our cable guys had a problem snaking the lines, I'm sure our plumber will have problems with this scenario too, as well as anyone else trying to do anything to the underside of the house.

I would open up only at the bearing beam areas in order to install solid blocking there. That would help laterally support the joist system when you next remove all the plaster and lath from underfloor.
When I dug under my 1910 house because of insufficient headroom, I devised a wagon with ropes on each end. With no steering , one could pull it out - loaded, and my sons could pull it back under to refill.
Be safe, G

Thanks for your reply. But I don't understand how to actually remove the drywall from the underside of the joists. Is it a matter of crawling under there and literally sawing the drywall out? I was told there are people who specialize in crawl-space type work.

Just wanting to get all my information straight before getting dirty under the house, in the dark, dust and cobwebs.

The issue I'm running into is this: is this really classified as foundation work? Because it might as well just be removing drywall from a wall, except it's the underside of the floor of the house... Like I said, I barely know where to begin with this one...